linux-kernel - Re: [PATCH v2 24/24] ext4: enable block size larger than page size

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Message-ID: <20251110151604.GE2988753@mit.edu>
Date: Mon, 10 Nov 2025 10:16:04 -0500
From: "Theodore Ts'o" <tytso@....edu>
To: libaokun@...weicloud.com
Cc: linux-ext4@...r.kernel.org, adilger.kernel@...ger.ca, jack@...e.cz,
        linux-kernel@...r.kernel.org, kernel@...kajraghav.com,
        mcgrof@...nel.org, ebiggers@...nel.org, willy@...radead.org,
        yi.zhang@...wei.com, yangerkun@...wei.com, chengzhihao1@...wei.com,
        libaokun1@...wei.com
Subject: Re: [PATCH v2 24/24] ext4: enable block size larger than page size

On Fri, Nov 07, 2025 at 10:42:49PM +0800, libaokun@...weicloud.com wrote:
> From: Baokun Li <libaokun1@...wei.com>
> 
> Since block device (See commit 3c20917120ce ("block/bdev: enable large
> folio support for large logical block sizes")) and page cache (See commit
> ab95d23bab220ef8 ("filemap: allocate mapping_min_order folios in the page
> cache")) has the ability to have a minimum order when allocating folio,
> and ext4 has supported large folio in commit 7ac67301e82f ("ext4: enable
> large folio for regular file"), now add support for block_size > PAGE_SIZE
> in ext4.
> 
> set_blocksize() -> bdev_validate_blocksize() already validates the block
> size, so ext4_load_super() does not need to perform additional checks.
> 
> Here we only need to add the FS_LBS bit to fs_flags.
> 
> In addition, allocation failures for large folios may trigger warn_alloc()
> warnings. Therefore, as with XFS, mark this feature as experimental.
> 
> Signed-off-by: Baokun Li <libaokun1@...wei.com>
> Reviewed-by: Zhang Yi <yi.zhang@...wei.com>

Could you add:

#ifdef CONFIG_TRANSPARENT_HUGEPAGES
EXT4_ATTR_FEATURE(blocksize_gt_pagesize);
#endif

in fs/sys/sysfs.c, so that userspace programs (like those in e2fsprogs
and xfstests) can test /sys/fs/ext4/features/... to determine whether
or not blocksize > pagesize is supported?  That way we can more easily
determine whether to test the 64k blocksize configurations in
xfstests, and so we can supress the mke2fs warnings:

mke2fs: 65536-byte blocks too big for system (max 4096)
Proceed anyway? (y,N) y
Warning: 65536-byte blocks too big for system (max 4096), forced to continue

... if the feature flag file is present.

Thanks!!

	 	    	       	       - Ted